The invention relates to a device for producing images of the earth or other heavenly body from a satellite or other space vehicle.
It is known to obtain spectral images of the Earth aboard a stabilized satellite by means of a dispersing system comprising a prism or a grating, or by means of filters or of dichroic blades.
U.S. Pat. No. 3,660,594 discloses a device comprising a plurality of prisms or gratings which spectrally disperse each of the image segments onto the photosensitive input surface of a suitable camera tube.
The resolution thus obtained is low and a group or a plurality of prisms must be used.
To avoid these drawbacks it has been proposed to use a single optical system, as disclosed in the U.S. Pat. No. 3,702,735.
This Patent discloses a device which essentially comprises a Michelson interferometer associated with an array of photodetectors. Means are provided for reciprocating one of the mirrors of the interferometer in order that each individual photodetector receives an interferogram signal which is functionally related to the spectrogram of light from the scene. The signals provided by the photodetectors are transfered to a computer wherein the signals are processed in a Fourier transform unit to provide the spectrogram.
The resolution is improved but it is very difficult aboard a space vehicle to control precisely the movement of the mirror of the Michelson interferometer.